Spinach Gratin

This recipe has become a staple of Thanksgiving at our house and a must-make every year.

Ingredients

• 4 tbsp (1/2 stick) unsalted butter
• 4 cups chopped yellow onions (2 large)
• 1/4 cup flour
• 1/4 tsp grated nutmeg
• 1 cup heavy cream
• 2 cups milk
• 3 lbs frozen chopped spinach, defrosted (5 ten-ounce packages)
• 1 cup freshly grated Parmesan cheese
• 1 tbsp kosher salt
• 1/2 tsp freshly ground black pepper
• 1/2 cup grated Gruyere cheese

Instructions

1. Preheat oven to 425°F.
2. Melt 4 tbsp butter in a heavy-bottomed pan over medium heat. Add 4 cups chopped onions and cook, stirring occasionally, until soft, roughly 15 minutes.
3. Stir in 1/4 cup flour and 1/4 tsp nutmeg, cooking for 2 minutes to toast the flour.
4. Pour in 1 cup heavy cream and 2 cups milk. Cook, stirring frequently, until the sauce thickens.
5. Squeeze all excess liquid from 3 lbs defrosted spinach and fold into the sauce.
6. Mix in 1/2 cup Parmesan cheese. Season with 1 tbsp salt and 1/2 tsp pepper, adjusting to preference.
7. Transfer mixture to a baking dish. Top with remaining 1/2 cup Parmesan and 1/2 cup Gruyere.
8. Bake for 20 minutes until bubbling and heated through. Serve immediately.